On 16/12/18 19:55, Eric Biggers wrote: > Hi Peng and Paolo, > > On Sun, Oct 21, 2018 at 12:01:55PM +0200, Paolo Bonzini wrote: >> On 20/10/2018 18:57, syzbot wrote: >>> Hello, >>> >>> syzbot found the following crash on: >>> >>> HEAD commit: 8c60c36d0b8c Add linux-next specific files for 20181019 >>> git tree: linux-next >>> console output: https://syzkaller.appspot.com/x/log.txt?x=12d808b5400000 >>> kernel config: https://syzkaller.appspot.com/x/.config?x=8b6d7c4c81535e89 >>> dashboard link: >>> https://syzkaller.appspot.com/bug?extid=f87f60bb6f13f39b54e3 >>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17cf2f5e400000 >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1036dcce400000 >>> >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>> Reported-by: syzbot+f87f60bb6f13f39b54e3@xxxxxxxxxxxxxxxxxxxxxxxxx >> >> Tentative (untested) patch: >> >> diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c >> index 3710342cf6ad..dc76cc8d24fd 100644 >> --- a/virt/kvm/coalesced_mmio.c >> +++ b/virt/kvm/coalesced_mmio.c >> @@ -90,6 +90,7 @@ static int coalesced_mmio_write(struct kvm_vcpu *vcpu, >> return 0; >> } >> >> +/* called with kvm->slots_lock held */ >> static void coalesced_mmio_destructor(struct kvm_io_device *this) >> { >> struct kvm_coalesced_mmio_dev *dev = to_mmio(this); >> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c >> index b20b751286fc..001e1ef18c8c 100644 >> --- a/virt/kvm/eventfd.c >> +++ b/virt/kvm/eventfd.c >> @@ -741,8 +741,8 @@ ioeventfd_write(struct kvm_vcpu *vcpu, struct >> kvm_io_device *this, gpa_t addr, >> } >> >> /* >> - * This function is called as KVM is completely shutting down. We do not >> - * need to worry about locking just nuke anything we have as quickly as >> possible >> + * This function is called as KVM is completely shutting down, so there >> + * are no RCU readers anymore. Called with kvm->slots_lock held. >> */ >> static void >> ioeventfd_destructor(struct kvm_io_device *this) >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index aff1242b7af7..e6f2ae6fedcd 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -783,6 +783,7 @@ static void kvm_destroy_vm(struct kvm *kvm) >> list_del(&kvm->vm_list); >> spin_unlock(&kvm_lock); >> kvm_free_irq_routing(kvm); >> + mutex_lock(&kvm->slots_lock); >> for (i = 0; i < KVM_NR_BUSES; i++) { >> struct kvm_io_bus *bus = kvm_get_bus(kvm, i); >> >> @@ -790,6 +791,7 @@ static void kvm_destroy_vm(struct kvm *kvm) >> kvm_io_bus_destroy(bus); >> kvm->buses[i] = NULL; >> } >> + mutex_unlock(&kvm->slots_lock); >> kvm_coalesced_mmio_free(kvm); >> #ifdef KVM_DIRTY_LOG_PAGE_OFFSET >> if (kvm->dirty_ring_size) >> > > This is still happening. Paolo, I don't see how your patch matches this bug, as > it has a single threaded reproducer. I simplified it to: > > #include <fcntl.h> > #include <linux/kvm.h> > #include <sys/ioctl.h> > > int main(void) > { > int kvm, vm; > struct kvm_coalesced_mmio_zone zone = { 0 }; > > kvm = open("/dev/kvm", O_RDWR); > > vm = ioctl(kvm, KVM_CREATE_VM, 0); > > ioctl(vm, KVM_REGISTER_COALESCED_MMIO, &zone); > > zone.pio = 1; > ioctl(vm, KVM_UNREGISTER_COALESCED_MMIO, &zone); > } > > The bug is in this commit: > > commit 0804c849f1df0992d39a37c4fc259f7f8b16f385 > Author: Peng Hao <peng.hao2@xxxxxxxxxx> > Date: Sun Oct 14 07:09:55 2018 +0800 > > kvm/x86 : add coalesced pio support > > The problem is that if you register a kvm_coalesced_mmio_zone with '.pio = 0' > but then unregister it with '.pio = 1', KVM_UNREGISTER_COALESCED_MMIO will try > to unregister it from KVM_PIO_BUS rather than KVM_MMIO_BUS, which is a no-op, > but then it frees the kvm_coalesced_mmio_dev anyway. > > Here's one possible fix but I don't know what was intended here. Are you > supposed to pass in the same value of '.pio' when unregistering or is it > supposed to use the existing value? Can one of you please point me to the > documentation for these ioctls? > > diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c > index 3710342cf6ad0..6855cce3e5287 100644 > --- a/virt/kvm/coalesced_mmio.c > +++ b/virt/kvm/coalesced_mmio.c > @@ -175,10 +175,14 @@ int kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm, > { > struct kvm_coalesced_mmio_dev *dev, *tmp; > > + if (zone->pio != 1 && zone->pio != 0) > + return -EINVAL; > + > mutex_lock(&kvm->slots_lock); > > list_for_each_entry_safe(dev, tmp, &kvm->coalesced_zones, list) > - if (coalesced_mmio_in_range(dev, zone->addr, zone->size)) { > + if (zone->pio == dev->zone.pio && > + coalesced_mmio_in_range(dev, zone->addr, zone->size)) { > kvm_io_bus_unregister_dev(kvm, > zone->pio ? KVM_PIO_BUS : KVM_MMIO_BUS, &dev->dev); > kvm_iodevice_destructor(&dev->dev); > Thanks for the patch, I queued it. Paolo
